XXE in The Opennms Group Horizon
CVE-2026-19596
An XML External Entity (XXE) vulnerability exists in the XML collector of multiple versions of OpenNMS Meridian and Horizon. When OpenNMS collects XML from a source whose response is attacker-controlled (for example a compromised monitored host or an HTTP man-in-the-middle position), the collector's XML parser resolves external entities and external DTDs. This allows an attacker to read files accessible to the OpenNMS service account, including database credentials, and to induce out-of-band requests. The solution is to upgrade to Meridian 2024.3.13, 2025.0.10 and Horizon 36.0.4 or newer. Meridian and Horizon installation instructions state that they are intended for installation within an organization's private networks and should not be directly accessible from the Internet.
Vulnerability class: XXE (XML External Entity)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 5.9 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N.
EPSS exploit prediction
EPSS: 0.003 (26.9th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 27th percentile — 26.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.003 · change: +0.001
Affected products
Weakness classification (CWE)
References
Frequently asked questions
- What is CVE-2026-19596?
- CVE-2026-19596 is a medium-severity vulnerability in The Opennms Group Horizon, classified under Improper Restriction of XML External Entity Reference (XXE). CVSS score: 5.9/10. Published 2026-09-10.
- How severe is CVE-2026-19596?
- Medium severity. CVSS v3 base score is 5.9 out of 10.